This is used to charge batteries on tractors and equipment that is not conveniently near a 110V power for a typical battery charger.

This has also been used very successful to power a electrolysis setup for rust removal.

Electrolysis pics from cleaning out a motorcycle gas tank. Electrolysis is very easy. Need 12V power supply (most use a battery charger but I burnt up a few trying this), a sacrificial piece of clean metal, and a tub for water and box of baking soda mixture. negative terminal goes to the rusty metal you want to clean and the positive to the sacrificial piece of clean metal. Make sure that they do not come in direct contact. I used a couple of rubber stoppers to isolate the sacrificial rod that I inserted inside the motorcycle gas tank. Submerged in water and add a box of baking soda. The rust will fly right off of the rusty part and stick to the sacrificial piece.

Check out electrolysis. This source is practical and concise. Be sure to read, understand and follow this and wear these- tap tap -safety glasses.Rust Removal using Electrolysis

by the way I'm a thinkin you lost your battery chargers since you used a steel barrel and put your negative (-) lead on the barrel causing a short circuit. The barrel is getting "plated" with rust. It should be the rebar or old saw blade or what ever iron (never stainless) you want the rust to go. If you search [rust removal by electrolysis] you will find many many sources some good, some academic and some practical like above.
JohnMTO